Age, metallicity, and [α/Fe] ratio versus σ. Open circles are the Coma dwarfs from Smith et al. (2009), filled circles are the low-density environment (LDE) dwarfs of this paper (we have excluded RR143_09192 and RR242_36267, which have a poor quality SSP fit, see Sect. 3.2, and RR216_12209, which is an Sc), while open triangles are the ETGs of A07. The solid and dotted lines are the least square linear fits to the (Coma dwarfs + A07) and (LDE dwarfs + A07) samples, respectively.